The present invention relates to a suspension control system.
One example of a conventional suspension control system is disclosed in Japanese Patent Application Unexamined Publication (KOKAI) No. 7-232530. The conventional suspension control system judges road surface conditions on the basis of the frequency of a signal detected by a vertical acceleration sensor. The term "road surface conditions" means conditions of each particular road, for example, an undulating road that causes a low-frequency vertical acceleration signal to be generated, or a bad road that causes a high-frequency vertical acceleration signal to be generated. Then, the suspension control system adjusts a control signal for an actuator in accordance with the result of the judgment of the road surface conditions, thereby allowing a shock absorber to generate a damping force according to the result of the judgment.
Incidentally, road surface conditions cannot clearly be classified into undulating roads, bad roads, normal roads, etc. Road surface conditions often have both an undulating road component and a bad road component. That is, there are many road surfaces that are both undulating and rough. In other words, there are many cases where when road surface conditions are detected with a vertical acceleration sensor, for example, the detected signal has a high-frequency component superimposed on a low-frequency component. In such cases, according to the above-described prior art, a road that is undulating and rough is judged to be either an undulating road or a bad road, and control adapted for only an undulating road or a bad road determined by the result of the judgment is carried out. Consequently, under circumstances where steering stability if important, control for a bad road may be carried out (i.e. damping force characteristics may be set "soft"), causing the vehicle steering stability to be impaired. Alternatively, under circumstances where ride quality should be given priority, control for an undulating road may effected (i.e. damping force for a characteristics may be be set "hard"), causing the ride quality to be degraded. Thus, the prior art is likely to fail to take full advantage of a predetermined degree of importance in the suspension control.